Fluid tanks are used for many purposes in vehicles. It is the main task to store a maximum amount of fluid whilst requiring a minimum installation space. Thereby, fluid tanks are designed in a very complex shape to use the installation space available. These tanks are also used in the hydraulic circuit of a vehicle, e.g. in agricultural machinery like a tractor, which is supplying the required oil to tractor-related consumers e.g. the front and rear lifting unit or to consumers which relate to attachments e.g. hydraulic cylinders lifting a plough. The performance of this hydraulic circuit is mainly influenced by the oil capacity of the tank which is limiting the delivery capacity of the pump to consumers. As these circuits are closed circuits, fluid is returning into the tank after supplying the consumers.
In addition to this, fluid tanks also serve to separate stored fluids, e.g. hydraulic or lubrication oil, from air which is brought into fluid systems during refilling or by consumers if the fluid is circulating inside a circuit. As air causes pump damage, e.g. cavitation, and reduce system performance this air has to be discharged to the atmosphere. Therefore, a port is provided which connects the tank to the atmosphere.
To avoid the discharge of fluid carried by the air to the environment, fluid separators (filters) are installed at these ports. These separators are equipped with porous filter elements, consisting of e.g. filter paper, non-woven material or wire mesh. All these materials have in common, that they are only capable of dealing with small amounts of fluid carried by the air known as fluid mist. If they are completely coated by the stored fluid, the pores of the filter element are blocked and the filter has to be changed. So it is also a requirement of a deaeration system to avoid complete washing of the separator/filter element with the stored fluid. This is achieved by installing the separator above in a top wall of the tank. Even if the filters are not washed completely it is necessary to exchange them from time to time.
Vehicles of the kind mentioned above, e.g. small and vineyard tractors, are designed to have short overall dimensions to be used for special jobs in narrow environments or on extreme inclined fields. Especially if it is necessary to drive at inclined hills perpendicular or along to the direction of inclination, the oil level in fluid tanks vary very much during operation.
It is also well known to use chassis or housing parts of such tractors as a reservoir for several fluids. This is very common for vehicles using hydrostatic or hydrostatic-mechanical torque split transmissions. As these transmission do not need a clutch to disconnect the engine from the transmission, the free space is used to storage fluids. The fluid can be hydraulic fluid which is used for transmission and/or the hydraulic circuit of a agricultural working machinery.
This integration into the vehicle requires a very complex tank design which is typically of a generally U-shaped configuration which is very difficult for deaeration systems.
Installing a number of separators in different positions increases the costs and maintenance work.